Surgical microscopes provide a magnified view of the operating field to the surgeon. Ophthalmic surgical microscopes are commonly stereo zoom microscopes with binocular view ports for the surgeon, and frequently have one or two observer view ports at ninety degrees (left and right) to the surgeon. The working distance between the objective lens of the microscope and the surface of a patient eye may range from about 100 mm to about 200 mm. At this working distance, which provides a suitable field of access for the manual work of the surgeon, the field of view within a patient eye may be quite limited. It is quite common to use an intermediate lens, such as the Binocular Indirect Ophthalmo Microscope (BIOM) of Oculus Optikgerat, to modify the magnification and field of view for the surgeon. This intermediate lens is mounted to the under-carriage of the microscope head, and includes mechanics to adjust focus, and to flip the lens into and out of the field of view of the microscope.
Other illumination or imaging devices may also be used in the surgical field. Ideally, all illumination and imaging sources would be directly integrated coaxial to and within the optical path of the operating microscope, without impacting the operating field for the surgeon, the observers, the anesthesiologists, and the like. It is still desirable to provide a readily maneuverable mount for imaging and other accessories that is closely coupled to the surgical field, utilizing the mechanical controls and attributes that are already integral to a well-functioning operating microscope, without degrading the visual attributes of the operating microscope.
A particular case of interest is the incorporation of optical coherence tomography (OCT) imaging into the surgical visualization practice. OCT provides high resolution imaging of ocular tissue microstructure, and is showing great promise to provide information to the surgeon that will improve therapeutic outcomes, and reduce the total economic burdens of surgery by reducing risk and reducing re-work.
Conventional Fourier domain OCT (FDOCT) systems will now be discussed to provide some background related to these systems. Referring first to FIG. 1A, a block diagram of an FDOCT retinal imaging system will be discussed. As illustrated in FIG. 1A, the system includes a broadband source 100, a reference arm 110 and a sample arm 140 coupled to each other by a beamsplitter 120. The beamsplitter 120 may be, for example, a fiber optic coupler or a bulk or micro-optic coupler. The beamsplitter 120 may provide from about a 50/50 to about a 90/10 split ratio. As further illustrated in FIG. 1A, the beamsplitter 120 is also coupled to a wavelength or frequency sampled detection module 130 over a detection path 106 that may be provided by an optical fiber.
As further illustrated in FIG. 1A, the source 100 is coupled to the beamsplitter 120 by a source path 105. The source 100 may be, for example, a continuous wave broadband superluminescent diode, a pulsed broadband source, or tunable source. The reference arm 110 is coupled to the beamsplitter 120 over a reference arm path 107. Similarly, the sample arm 140 is coupled to the beamsplitter 120 over the sample arm path 108. The source path 105, the reference arm path 107 and the sample arm path 108 may all be provided by optical fiber or a combination of optical fiber, free-space, and bulk- or micro-optical elements.
As illustrated in FIG. 1A, the reference arm of the FDOCT retinal imaging system may include a collimator assembly 180, a variable attenuator 181 that may include a neutral density filter or a variable aperture, a mirror assembly 182, a reference arm variable path length adjustment 183 and a path length matching position 150, i.e. optical path length matching between the reference arm path length and the sample arm path length to the subject region of interest. As further illustrated, the sample arm 140 may include a dual-axis scanner assembly 190 and an objective lens with variable focus 191.
The sample illustrated in FIG. 1A is an eye including a cornea 195, iris/pupil 194, ocular lens 193 and retina 196. A representation of an FDOCT imaging window 170 is illustrated near the retina 196. The retinal imaging system relies on the objective lens plus the optics of the subject eye, notably cornea 195 and ocular lens 193, to image the posterior structures of the eye. As further illustrated the region of interest 170 within the subject is selected through coordination of the focal position 196 and reference arm path length adjustment 183, such that the path length matching position 197 within the subject is at the desired location.
Referring now to FIG. 1B, a block diagram illustrating a FDOCT corneal (anterior) imaging system will be discussed. As illustrated therein, the system of FIG. 1B is very similar to the system of FIG. 1A. However, the objective lens variable focus need not be included, and is not included in FIG. 1B. The anterior imaging system of FIG. 1B images the anterior structures directly, without reliance on the optics of the subject to focus on the anterior structures.
As discussed above, ophthalmic surgical microscopes can provide surgeons a magnified view of various areas of the eye on which they are operating. However, there are many ophthalmic surgical procedures that may benefit from the kind of high-resolution depth-resolved imaging provided by Optical Coherence Tomography (OCT). Thus, integrating an OCT system into a surgical microscope may provide greater capabilities and enable procedures that currently cannot be performed with conventional stereoscopic imaging.
As illustrated in FIG. 1C, there are various regions of interest in the eye, which may require different OCT imaging characteristics. For example, referring to FIG. 1C, region 1, the corneal region, typically requires relatively high resolution OCT imaging. A fairly large depth-of-focus (DOF) is desirable to allow the entire corneal structure to be imaged. Such imaging is desirable in support of cornea transplant procedures. Likewise, imaging of the crystalline lens, region 2, benefits from high resolution imaging of the capsular structure. A large DOF is required to visualize the entire lens at one time. By contrast, structures on the retina, region 3, lie in a constrained depth region, and tend to be very fine. Thus, retinal imaging typically requires very high resolution, but not necessarily a large DOF.
Existing surgical microscopes incorporating OCT will be discussed with respect to FIGS. 1D and 1E. Referring first to FIG. 1D, like reference numerals refer back to FIGS. 1A and 1B. However, as illustrated in FIG. 1D, a stereo zoom microscope 160 has been incorporated into the sample arm path 108. As illustrated, the surgical microscope 160 includes two oculars (binocular view ports) 162 for the surgeon to view the sample 199. The surgical microscope 160 of FIG. 1D includes a beamsplitter 161, where the beamsplitter may be a dichroic filter, and an objective lens 163 positioned beneath the dichroic filter 161. As further illustrated the sample arm path 108 is coupled to a collimator 165 that forms a beam exiting an optical fiber and a pair of galvos 190 which directs the beam to the dichroic filter 161 integrated into the infinity space of the microscope between the ocular paths 162 and the main objective 163. The beam reflects off the dichroic filter 161 and through the objective lens 163 to image the sample 199, which may be an eye or any other accessible region of a subject. The microscope 160 illustrated in FIG. 1D is a static surgical microscope, i.e. dynamic adjustments to the focal lengths are not possible; focal changes are possible only by exchange of optical elements (installing a new main objective lens 163) or changing the working distance between the microscope 160 and the subject 199.
Referring now to FIG. 1E another design of a surgical microscope incorporating OCT will be discussed. Surgical microscopes illustrated in FIG. 1E are discussed in U.S. Pat. No. 8,366,271 to Izatt et al., the disclosure of which is incorporated herein by referenced as if set forth in its entirety. As illustrated in FIG. 1E, the surgical microscope system of FIG. 1E is similar to the system of FIG. 1D except a telescope lens assembly set 167 is provided between the pair of galvos 190 and the dichroic filter 161 of the surgical microscope 163. Thus, in the system of FIG. 1E, the beam travels through the galvos 190 into the telescope lens set 167 and then through the dichroic filter 161 through the objective lens 163 to image the sample 199. The presence of the telescope lens set 167 provides beam shaping to maximize the numerical aperture of the system, potentially improving the lateral resolution of the images produced by the system, however, the system illustrated in FIG. 1E offers limited flexibility in modifying or controlling the characteristic of the scanning beam. Surgical microscopes are tailored to provide clear optical view to the subject, with uniform illumination and accurate color temperature. Stereo microscopes provide a degree of parallax to provide the surgeon with a sense of space and topography. Occasionally dyes are used to emphasize topography. High definition video is being offered into surgical microscopes to improve visual clarity. Topographic 3D video technologies adopted from entertainment industry, such as polarization-diversity stereoscopy, are now being added to increase the sense of depth.
Such surgical stereo microscopes are constrained to surface visualization. Optical coherence tomography (OCT) is now a well-established technology for imaging beneath an optically translucent surface. High resolution OCT offers a capability to observe sub-surface structures, complementary to the surface views of stereo, high definition and three dimensional surgical microscopes. Optical coherence tomography is a standard of care in retinal diagnostics, and is finding some use in cornea imaging and metrology. OCT is only beginning to find use in intra-surgical imaging. A handheld ophthalmic OCT system (offered by Bioptigen, Inc.) that is CE marked to the Medical Device Directive and has been FDA cleared for imaging patients under anesthesia. This device is finding application in handheld and mounted configurations for structural imaging during ophthalmic surgeries, including retinal surgery and cornea transplant surgery and an adjunct to surgeon's microscope visualization.
Early results with OCT imaging during retinal and cornea surgery has demonstrated that surgical procedures have direct and immediate impact to tissues that is not visible with traditional microscope imaging optics. It is desirable therefore to visualize the surgical procedure simultaneously with a traditional surface microscope image and the depth-resolved capability of optical coherence tomography using a heads up display.